Recently, the organic light emitting diode (OLED) displayer is one of the hotspots in the research field of flat-panel display. Compared to a liquid crystal displayer (LCD), the OLED has advantages such as low energy consumption, low production cost, self-illumination, wide viewing angle and fast response. Nowadays, in the fields such as mobile phone, personal digital assistant (PDA), digital camera, the OLED starts to take the place of the traditional LCD. The design of a pixel circuit is a core technology for the OLED displayer and has important research significance.
Different from the LCD in which the brightness is controlled using a stable voltage, the current-driven OLED needs a stable current to control light emit. Due to manufacture process and aging of the device, a threshold voltage Vth of the driving transistor in the pixel circuit may not be uniform, causing varying current passing through OLEDs at pixel points and uneven display brightness and affecting whole display effect of image.